The problem of either ascertaining the identity of an individual or ascertaining whether an individual is the person he or she says, is a common one faced every day by industry, businesses, and government. There are three accepted fundamental ways that a person's identity may be established: (1) something the person knows; (2) something the person has; or (3) something the person is. Category (1) includes such items as passwords, knowledge of the combination of a lock, or knowledge of a series of facts from the individual's personal background. Category (2) includes identification cards, passes, badges, and keys to locks. Category (3) includes physical characteristics of the individual such as fingerprints, hand geometry, voice characteristics, physical appearance, and physical deformities such as scars and the like. An evaluation of the three fundamental ways quickly directs the practical, real-time applications when user acceptance, practicality, and liability are considered, to digital minutiae correlation of fingerprints.
Fingerprints have been found to be unique to the individual and therefore provide an extremely reliable identification characteristic, have been found to be extremely practical to be used for identification and, if not recorded, are generally not objectionable as a means for identification by either the individual to be identified or the organization using the system. Conventional systems which have attempted to use fingerprints for such identification are as diverse as that disclosed in the Nielsen U.S. Pat. No. 2,936,607 (for operating a lock mechanism), to that disclosed in the Williams et al U.S. Pat. No. 3,201,961 (operating a door mechanism), to that disclosed in the Ernst U.S. Pat. No. 3,576,537 and the Miller and Miller et al U.S. Pat. Nos. 3,576,538 and 3,584,958 (for comparing an individual's fingerprint with a representation thereof on a record such as an identification card), and finally to that such as disclosed in the McMahon U.S. Pat. No. 3,975,711 (comparison of the fingerprint pattern on an individual's finger with a representation of the fingerprint electronically stored in a computer), all of said patents being incorporated herein by reference.
Because of the tremendous advances in the computer industry, there are numerous conventional systems presently available or disclosed in the prior art which permit a real-time identification of a fingerprint pattern. For example, the Federal Bureau of Investigation uses an automatic fingerprint identification system entitled "FINDER". This system was developed with background support done by the National Bureau of Standards and with contracts with the Calspan Corporation and North American Rockwell Corporation. Thc FINDER system utilizes an optical scan reader which scans a fingerprint ink image and develops an analog signal dependent upon the reflectivity of the ink image as the scan dot proceeds in the scan. The information is analyzed by a programmed computer to enhance the image electronically by eliminating gray areas and develop a digitized black and white image of the fingerprint in the computer memory. The programmed computer also fills in gaps in the ridges which are less than a prescribed length and eliminates spots in the valleys which are shorter than a prescribed length. A 16 by 16 increment square window scans the fingerprint, an increment being a tenth of a millimeter. Thus, the window advances through the fingerprint in increments of a tenth of a millimeter and looks for ridges which enter the square window, but do not exit it. When such a ridge is identified, its coordinate location is stored in the computer memory and the ridge is also analyzed to establish an angle, theta, of the ridge at the termination. The data is then converted so that the black ridges and white valleys are reversed as to color and the data is rescanned to look for terminations of valleys (which are ridge bifurcations). The additional coordinates and angles for each of the inverted ending points are also stored.
The FINDER system uses an analysis technique which considers the coordinates and angle values of the minutiae and compares them against other coordinates and angle values of stored fingerprints. The analysis technique was developed by the National Bureau of Standards and is explained and described in National Bureau of Standards NBS Technical Notes 538 (issued August, 1970), 730 (issued June, 1972), and 878 (issued July, 1975), incorporated herein by reference. However, the FBI FINDER system is very elaborate and is aimed at storing extremely huge numbers of fingerprint data. Thc FINDER system is more complex than that needed when the object is merely to compare an individual's fingerprint with that of the person he claims to be. In addition to being very elaborate, the FINDER system is extremely expensive, costing well over a million dollars.
The commercially available Calspan system is called "FINGERSCAN", and is an automatic fingerprint recognition system for access control and identification. This system combines a number identification system with a fingerprint reader and scans the person's fingerprint, comparing the scanned image minutiae pattern with a stored pattern identified by the number. An associated computer digitizes the information, enhances the image and develops the minutiae location using a method similar to the FINDER system. This system uses extremely complex equipment and therefore is also rather expensive, a terminal station reported as selling for approximately $20,000 with an additional charge for the remote computer.
Other, less costly approaches, such as that marketed by KMS Industries Inc. reportedly do not have the high reliability of those techniques which use minutiae. The KMS system makes a laser scan of a fingerprint to develop a hologram and compares the developed hologram with a previously stored image or one mounted on an identification card. The problems of a holograph type system and thc operation of such a system are disclosed in numerous U.S. patents such as those of Caulfield et al U.S. Pat. No. 3,716,301 and Malloney U.S. Pat. No. 3,743,421.
It appears that the major difficultics and disadvantages of the FINGERSCAN and FINDER systems and other systems disclosed in the prior art is the cost of hardware and real time required to reliably enhance and examine the fingerprint image and establish the minutiae locations given the low quality level of the fingerprint image with which they must work. Furthermore; in those systems which use latent prints, while the distances between the ridges of a fingerprint averages 0.4 millimeters, they can vary by a factor of 2 for any individual finger depending on skin displacement when the finger contacts the hard surface normally encountered to establish a print which will be examined. Such a variation imposes extreme problems for a lowcost minutiae reader. Another factor in the prior art systems is the cost and time required for data processing, the FINDER system requiring large, general purpose digital computers.
Another apparent reason for the complexity of the prior art systems, and hence the amount of their cost and real time required to process an image, is that the location of the minutiae is defined not only by Cartesion Coordinates, but also by the angle of the ridge or valley producing the minutiae. For example, the Bodez U.S. Pat. No. 3,582,889, discloses a serial, first-in first-out processing of video signals which, however, must be interrupted so that the singular point detector can cycle a predetermined number of data points in a "window matrix" of the larger matrix. This system's approach not only requires a delay in processing the information, but also has an added circuit complexity. These deficiencies are also seen in the system disclosed in the Bourne U.S. Pat. No. 3,292,149. Both Bodez and Bourne patents are incorporated herein by reference.
However, it is believed that the major difficulty with all of the prior art devices is their inability to obtain a high quality, undistorted, reproducible fingerprint image. The quality of fingerprint images vary greatly in contrast and clarity. Furthermore, the widths of the ridges and of the valleys of different impressions of different fingerprints vary widely when such impressions are made on an unyielding surface or upon one which imposes shear loading on the finger during the impression act. This is particularly so when the shear loading varies during the impression act. Almost all of the prior art systems disclose the taking of a "live print" of a finger when the finger of the individual directly contacts the viewing window or prism. With this method, because the valleys of the fingerprint do not touch the glass and the ridges do contact the glass, the fingerprint is observable as a result of the different indicies of refraction of the contacted and non-contacted portions of the window. Surface contamination of the window results from repeated use and degrades the image quality. Finger pressure is uneven from point to point in the fingerprint area and results in "gray" areas in the image. Variation in shear forces as the finger is brought into contact with the window stretches portions of the fingerprint area and compresses other areas in a non-isotropic fashion causing significant distortion of the resulting image. As mentioned above, the prior art systems do not attempt to overcome this inadequacy by providing a higher quality print, but by utilizing expensive, real time computers and computer programs to reconstruct and enhance the fingerprint image.